1. Field of the Invention
This invention relates to peak respiratory flow monitoring. More specifically, this invention relates to peak flow monitoring of individuals with obstructive respiratory diseases and other conditions and includes apparatus for, and methods of, using this technique in the home and office as well as enhancing patient and physician access to calculated medical data computed therein.
2. Statement of the Art
Peak respiratory flow monitoring of patients with obstructive respiratory diseases or conditions, such as asthma, has been available for many years. Inexpensive mechanical peak flow meters have been used for patient home and office use and many patients have been taught to record their daily peak flow values and their symptoms in a personal diary. The physician then reviews the entries in a patient""s diary during regular office visits.
Monitoring of peak respiratory flow helps a patient to manage his or her condition. Generally, peak flow values below 80% of the patient""s personal best are an indication that the patient needs more medication or a change in medication to control his or her condition. Peak flow values below 50% of a patient""s personal best indicate that the patient should seek medical help immediately.
In measuring and monitoring peak flow, certain pressure data are calculated and evaluated in the form of pulmonary function parameter values. For example, Peak Expiratory Flow (PEF) is the fastest rate at which a person can exhale air out of the lungs after inhaling as large a volume of air as possible. Forced Expiratory Volume (FEVt) is the largest volume of air a person can exhale from the lungs over a time interval, xe2x80x9ct.xe2x80x9d FEV1 is the largest volume of air that a person can exhale from the lungs in one second. Finally, Forced Vital Capacity (FVC) is the largest volume of air a person can exhale from the lungs after a full inspiration, using maximal effort.
Conventional, state-of-the-art equipment used for pulmonary function testing is expensive and requires special training for effective use. Therefore, it is impractical to send pulmonary function testing equipment home with a patient. In response to the perceived need for home monitoring, the aforementioned mechanical peak flow meters were developed to provide a way for the patients to monitor certain elements of respiratory function at home on a daily basis. However, mechanical peak flow meters exhibit substantial deficiencies. Those problems include poor initial accuracy that only worsens as the product ages, difficult-to-read PEF scales that impair reading accuracy, and the inability to integrate gas flow over time to estimate volume related parameters, such as FEV1 or FVC.
Recently, electronic peak flow meters have become available for patient home and office use. These devices typically include the capability to calculate additional parameters associated with a forced vital capacity (FVC) maneuver, such as FEV1. These devices will typically have internal non-volatile memory for storing the PEF and FEV1 results.
Most electronic peak flow meters also provide a red-yellow-green zone respiratory flow indicator. A xe2x80x9cgreenxe2x80x9d zone indicates that a peak respiratory flow value is above 80% of a patient""s personal best, or predictive, norm. A yellow zone indicates values above 50% and a red zone, values below 50%. Use of these zones facilitates recognition by the patient and physician of the patient""s condition to indicate appropriate treatment for the patient.
In addition, some electronic peak flow meters provide a means to enter patient symptoms and/or medication usage. The entered information is stored in the device""s memory as a part of data included in an xe2x80x9celectronic diary.xe2x80x9d The means for symptom and medication entry on existing peak flow meters are extremely limited in flexibility and require the patient to remember numbers or symbols associated with different symptoms.
Furthermore, a peak flow meter flowhead which is easily removable and replaceable by a patient is not believed to be present in conventional devices. The flowhead is the tube through which a patient exhales for measuring and monitoring certain peak flow pressure data. The flowhead can become partially occluded from repeated usage, with the device consequently losing its ability to accurately measure the increased pressure created inside the tube during exhalation. Thus, an easily removable flowhead that can also be easily cleaned or stored between readings so as to prevent such loss in accuracy is needed.
Further, conventional electronic peak flow meters employing pressure transducers exhibit an undesirable magnitude of internal volume extending between the aperture or pressure tap opening into the flowhead and the transducer employed to sense pressure generated therein, thus reducing the sensitivity of these devices. In addition, tubing conventionally used to connect the flowhead to the transducer may collect moisture or otherwise become obstructed from the patient""s exhalations therein, also impairing operation.
In accordance with the present invention, a peak respiratory flow monitoring system and methods of use are provided for monitoring patients with obstructive respiratory diseases or conditions, such as asthma. The system comprises a microprocessor-equipped base unit and a flowhead connected by a snap-fit therein. The base unit is capable of customizing reconfigurable text-based display messages storable in non-volatile memory and further comprises a pressure transducer housed within the base unit and located immediately adjacent a port in a receptacle on the base unit exterior. The flowhead is designed to be rollingly secured in the receptacle, and secured disposition of the flowhead in the receptacle results in a compression-type pneumatic connection and seal between the flowhead and the pressure transducer of the base unit. When such connection and seal is effected, a pressure generated in the flowhead can be communicated to the pressure transducer within the base unit and corresponding respiratory flow computed by the microprocessor while minimizing internal excess or xe2x80x9cdeadxe2x80x9d system volume by substantially eliminating any significant passage distance between the flowhead and the pressure transducer. The rolling connection and pneumatic seal between the flowhead and the pressure transducer of the base unit is effected by inserting a tab on the flowhead exterior with a corresponding slot in the wall of the receptacle while substantially concurrently rolling the flowhead to align a nipple on the flowhead exterior with the port in the wall of the receptacle and compress a gasket between the nipple and the pressure transducer within the base unit aligned with and immediately adjacent the port.
A method of using the peak flow monitoring system to monitor patients with obstructive respiratory diseases or conditions according to the present invention may be characterized, by way of example, as follows. First, a flowhead is rotatingly connected to a receptacle on the exterior of a base unit while a tap on the flowhead is concurrently operably and directly connected to a pressure transducer housed within the base unit via an intervening gasket surrounding a nipple on the flowhead aligned with a port in the wall of the receptacle. This connection forms a pneumatic seal between the flowhead and pressure transducer with minimal dead volume. Next, a pressure is generated in the flowhead by the patient""s respiratory (expiratory) flow therethrough, such pressure being communicated between the nipple and the port and through the gasket to the pressure transducer, the output of which is employed by the microprocessor in computing pulmonary function parameter values. These computed pulmonary function parameter values may then be either displayed as messages on a display, stored in a non-volatile memory, or retrieved and played back from memory using a keypad. Additional information can also be inserted into the base unit using the keypad for display as another display message on the display, stored with other display messages in the non-volatile memory, or retrieved using the keypad. In addition, an interface is provided for reconfiguring the display messages using an external host device such as a personal computer. Finally, the flowhead can be rotatingly disconnected from the receptacle and the base unit for cleaning or storage purposes.